It has long been known that nickel catalyzes the displacement of a butyl group as butene from a butyl aluminum by ethylene (K. Ziegler, Brennstoff Chem., 35, 321 (1954)). The mechanism of this catalysis has been extensively studied (K. Fischer et al. "Angewandte Chemie" 12 No. 12 pages 943-953 (December 1973)). It has been proposed that the trialkyl aluminum reduces the nickel compound to Ni metal which reacts with the .alpha.-olefin to form an olefin complex which reacts with trialkyl aluminum to displace the alkyls bonded to aluminum in an equilibrium reaction.
The nickel catalyzed alkyl displacement has not achieved commercial significance because the catalyst is extremely difficult to remove from the product and its presence causes undesirable side reactions. These side reactions are reverse displacement, isomerization and branched chain formation (Poe et al., Symposium on Production and Use of Alpha Olefins, Div. of Petrol. Chem., Am. Chem. Soc., Los Angeles, Mar.31-Apr.5, 1963). Poe et al. attempted to circumvent this problem by using a heterogenous catalyst system with nickel deposited on a support such as alumina. They reported high initial displacement activity which sharply declined after 4-8 hours and could not be reactivated.
Davis et al., U.S. Pat. No. 3,391,219, resorted to non-catalytic thermal displacement of alkyls of trialkyl aluminum with .alpha.-olefins. Displacement temperatures in the range of 280.degree.-320.degree. C. were required to effect the displacement followed by rapid cooling to about 120.degree. C. to minimize isomerization and other side reactions of the effluent .alpha.-olefin stream. Although very effective, this process suffers from the high energy consumption required by the high displacement temperature followed by the rapid cooling.
From the above it can be seen that a need exists for a process that can take advantage of the low temperature displacement temperatures made possible by the use of nickel catalysts while avoiding the undesirable side reactions encountered in the past with the use of nickel catalysts.